Solvatochromism as a mechanism for controlling intercomponent photoinduced processes in a bichromophoric complex containing [Ru(bpy)3]2+ and [Ru(bpy)(CN)4]2– units
作者:Naomi R. M. Simpson、Michael D. Ward、Angeles Farran Morales、Francesco Barigelletti
DOI:10.1039/b201597h
日期:2002.6.7
The dinuclear complex [(bpy)2Ru(μ-L1)Ru(CN)4] (1) contains Ru(bpy)3}2+-type (Ru-bpy) and Ru(bpy)(CN)4}2â-type (Ru-CN) chromophores covalently linked by a short, saturated âCH2OCH2CH2OCH2â chain. Since the photophysical properties of the Ru-CN chromophore are strongly solvent-dependent, whereas those of the Ru-bpy chromophore are not, it follows that altering the solvent provides a means of altering the driving force for inter-component photoinduced energy- or electron transfer processes. At room temperature, in a mixed solvent system varying from pure water to pure dmso, the characteristic luminescence of the excited Ru-bpy unit is progressively quenched as the proportion of dmso in the mixture increases. This behaviour
is consistent with both *Ru-bpy
â
Ru-CN energy transfer quenching and with Ru-CN
â
*Ru-bpy electron transfer quenching, because as the proportion of dmso in the solvent increases, the 3MLCT excited state of the Ru-CN unit drops in energy (which facilitates the energy transfer process) and its Ru(III)/Ru(II) reduction potential also becomes less positive (which facilitates the electron transfer process). Consideration of the solvent composition at which luminescence quenching of Ru-bpy by Ru-CN occurs, the saturated nature of the spacer, and the metalâmetal separation, collectively point towards Förster energy transfer being the quenching process which is switched on by the change in solvent composition. In contrast, at 77 K (frozen solvent) the 3MLCT state of the Ru-CN unit is raised in energy above that of the Ru-bpy unit, such that
the energy transfer gradient is reversed and *Ru-CN
â
Ru-bpy energy-transfer occurs with strong emission from the Ru-bpy terminus.
二核复合物[(bpy)2Ru(μ-L1)Ru(CN)4] (1) 包含以短的饱和 –CH2OCH2CH2OCH2– 链共价连接的 Ru(bpy)3}2+-型 (Ru-bpy) 和 Ru(bpy)(CN)4}2--型 (Ru-CN) 发色团。由于 Ru-CN 发色团的光物理性质强烈依赖于溶剂,而 Ru-bpy 发色团的性质则不然,因此改变溶剂可以改变组分间光诱导能量或电子转移过程的驱动力。在室温下,在从纯水到纯 DMSO 的混合溶剂系统中,随着混合物中 DMSO 比例的增加,激发 Ru-bpy 单元的特征发光逐渐被猝灭。这种行为与 *Ru-bpy → Ru-CN 能量转移猝灭和 Ru-CN → *Ru-bpy 电子转移猝灭一致,因为随着 DMSO 在溶剂中比例的增加,Ru-CN 单元的 3MLCT 激发态能量下降(这促进了能量转移过程),其 Ru(III)/Ru(II) 还原电位也变得不那么正(这促进了电子转移过程)。考虑到 Ru-CN 对 Ru-bpy 进行猝灭发光的溶剂组成、间隔链的饱和性质和金属–金属间隔距,综合指向了 Förster 能量转移是由于溶剂组成变化而开启的猝灭过程。相反,在 77 K(冷冻溶剂)条件下,Ru-CN 单元的 3MLCT 状态能量高于 Ru-bpy 单元,从而能量转移梯度反转,*Ru-CN → Ru-bpy 能量转移发生,且 Ru-bpy 端部强烈发光。